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"The gun lobby may be holding Congress hostage right now, but they do not have to hold America hostage," the president said

Some people might say the measures "might not have stopped the last massacre or the one before that or the one before that, so why bother trying?" President Obama said Tuesday. "I reject that thinking. We know we can't stop every act of violence, every act of evil. But maybe we can stop one act or violence, one act of evil."

Despite presenting them in relatively modest terms, Obama's directives — to reallocate resources, clarify rules and redouble existing efforts — could go a long way toward addressing issues that were at play in some of the high-profile mass shootings of the past decade, and a slew of other gun-related problems.

Of course, it's impossible to say whether any particular tragedy could or would have been prevented if Obama's rules had been in effect. But these examples do shed light on some of the loopholes in U.S. gun laws that Obama is seeking to fix.

1. The FBI will hire 230 additional personnel to process background checks, increasing its numbers in that arena by 50 percent. The agency is also partnering with the U.S. Digital Service to modernize its systems so it can process background checks 24 hours a day, seven days a week.

Why this matters: Two months before the 2015 shooting at Emanuel African Methodist Episcopal Church in Charleston, South Carolina, gunman Dylann Roof was arrested for possession of the drug Suboxone. That charge would have disqualified him from purchasing a gun if examiners from the FBI-run National Instant Criminal Background Check System, or NICS, had processed his application in time to catch it. Instead, the three-day waiting period imposed on firearms dealers in the U.S. expired without a decision, which meant that under federal law Roof was allowed to buy the .45-caliber Glock 41 he used to kill eight parishioners and the church's pastor, state Sen. Clementa Pinckney, during a Bible study session.

2. The federal Bureau of Alcohol, Tobacco and Firearms will upgrade it systems and expand personnel, too. The ATF is budgeting $4 million to improve its ballistics database — to find links between crimes that take place in multiple jurisdictions — and will hire 200 new agents to enforce gun laws.

Obama also clarified the penalties dealers can face for violating those laws (for instance, for selling without a license or failing to conduct background checks): up to five years in prison and $250,000 in fines. And he clarified that the licensee shipping a gun is responsible for notifying law enforcement if the gun goes missing.

Why this matters:According to the White House, in the last half decade an average of 1,333 guns recovered in criminal investigations every year are traced back to a licensee who claimed he or she never received the gun, but who also failed to report the weapon lost or stolen.

3. On Monday, Attorney General Loretta Lynch directed 93 U.S. attorneys to focus their resources on prosecuting gun crimes, with special attention paid to cases concerning "violent offenders, illegal firearms traffickers, and dangerous individuals who bypass the background check system to acquire weapons illegally."

Why this matters: During the push for increased gun regulations after the 2012 shooting at Sandy Hook Elementary School in Newtown, Connecticut, NRA president Wayne LaPierre told Congress that the U.S. didn't need new gun laws — it needed to use the ones it had. "Prosecuting criminals who misuse firearms works," LaPierre said. "Unfortunately, we've seen a dramatic collapse in federal gun prosecutions in recent years." To a certain extent, he was right: According to a 2013 Syracuse University study, gun prosecutions dropped under Obama's administration, compared to George W. Bush's.

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4. Lynch also issued a letter to the states emphasizing the importance of reporting "complete criminal history records and criminal dispositions, information on persons disqualified for mental health reasons, and qualifying crimes of domestic violence" to the federal government.

Why this matters: The shooter in the 2007 Virginia Tech massacre, Seung-Hui Cho, passed two separate federal backgrounds checks in order to buy the two guns he used to kill 32 people and wound 17 others. The Brady Center to Prevent Gun Violence argued in the aftermath of the shooting that Cho shouldn't have passed either background check since a Virginia court ruled he was a danger to himself two years earlier. It's the state's responsibility to report "mental defectives" to the federal government; after Virginia Tech, Congress passed legislation incentivizing states to make more of their records available to NICS.

The same principle applies for cases of domestic violence. Last year, 15-year-old Jaylen Fryberg used a .40-caliber Beretta handgun, purchased by his father, to shoot four classmates and himself. The father, Raymond Lee Fryberg Jr., would have been prevented from buying the gun if the state of Washington had reported the fact that he was the subject of a domestic violence restraining order years earlier.

5. Among the directives AG Lynch issued Monday was one asking U.S. attorneys' offices around the country to "renew" their efforts to combat domestic violence and keep abusers from buying guns.

Why this matters: Domestic violence and gun violence go hand-in-hand; the risk of homicide is 20 times higher in homes where both a gun and a history of domestic violence are present, and abused women are five times more likely to be killed by their abuser if that abuser owns a firearm.

6. There are various methods to avoid background checks: one is to purchase a gun through a legal entity. Obama's executive orders change an ATF rule to require background checks for people trying to buy weapons and other items through a trust or corporation.

Why this matters: Former LAPD officer Christopher Dorner purchased through a trust the rifle and silencers he used to kill four people and himself during a weeklong rampage that terrorized three Southern California counties in 2013. Dorner wrote in his manifesto that all he needed to create the trust was access to the accounting software Quicken and $10 for a notary.

7. Other ways to circumvent background checks include buying guns at gun shows and through some online retailers. Obama took a step to fix that on Monday by clarifying ATF rules to ensure all gun dealers — even those selling a small number of guns, and those selling online or at gun shows — obtain a license and conduct background checks.

Why this matters: Both James Holmes, the 2012 Aurora movie theater shooter, and Seung-Hui Cho purchased over the Internet the guns and ammunition they used during their shooting sprees. (That said, they both also passed background checks — despite their documented histories of mental health issues.)

8. Obama asked the Social Security Administration to make sure Americans who have been deemed a danger to themselves or others, and those who are receiving benefits for mental health conditions, be entered into the federal background check database. He directed the Department of Health and Human Services to issue a directive confirming that states would not be violating privacy laws if they reported mental health issues to the federal database. Obama also proposed devoting $500 million toward expanding access to medical help for the mentally ill.

Why this matters: Gun advocates often say that the problem with gun violence is not access to weapons, but mental illness. In fact, an analysis of 21 studies found people who have mental illnesses are four times more likely to be the victims of violence than those who don't. Increased access to mental-health services could benefit both the would-be victims and would-be perpetrators of gun violence.

9. Finally, Obama announced Monday that he is directing the Departments of Defense, Justice and Homeland Security to increase research and development to make it easier to track lost and stolen guns, and harder to use someone else's weapon or to accidentally discharge a gun.

Why this matters: Last year alone, 1,943 Americans were killed in accidental shootings, according to the nonprofit Gun Violence Archive.